The invention pertains to an actuating device for a tool or a workpiece tensioning jack in a machine tool spindle.
The working spindles of machine tools or processing centers as a rule have an integrated tool tensioning jack for automatic tensioning and release of the processing tools. In the conventional tool tensioning jacks, the tools are usually held by a tensioning grasper which is located at the front end of a tensioning rod which is tensioned by a cup spring packet and engages in a corresponding tightening bolt of the tools or tool holder. To release the tools, the tensioning rod is displaced by a usually hydraulically actuated piston-cylinder unit opposite the tensioning force of the cup spring packet, so that the tensioning jaw is opened and the tool is released. Often an inner coolant inlet is provided so that the lubricating coolant can be directed to the tool, for example, via the hollow tensioning rod through the interior of the working spindle. But in this case, the lubricating coolant has to be sent through a suitable device from a stationary connecting piece into the rotating parts during the processing. As a rule, this occurs through so-called rotary lead throughs, in which the transition between the fixed and rotating parts takes place by means of sealing rings that slide upon each other. In order to achieve a particularly space-saving and compact design, the rotary lead through can be integrated within the actuating device for the tool tensioning jack. However, since this kind of rotary lead through is not entirely leak-proof and leakage of the lubricating coolant may occur in particular at the connecting point between the stationary and rotating parts, the problem that occurs primarily in the compact design is to ensure a suitable removal of the leakage fluid.
From DE 195 43 612 C1 a similar actuating device is known for a tool or workpiece tensioning jack which contains a pressure piston which is arranged inside a housing for actuating the tensioning rod which is pretensioned by a set of springs. Integrated into this actuating device there is a rotary lead through which contains a first slide washer joined with the tensioning rod, and a second slide washer located in a separate sealing part. The pressure piston designed as ring piston is located in a cylinder that will move axially in a fixed machine part. If the ring piston is placed under pressure within the cylinder, then the piston will be braced against the spindle by means of internal engaging elements and exert a corresponding counter-force on the axially moving cylinder. In this manner, the tension rod and also the rotary lead through will be moved along.
It is the purpose of the invention to create a compact and space-saving actuating device of the kind described above, which makes possible a simple removal of leakage fluid.
The invention relates to an actuating device for a tool or a workpiece tensioning jack in a machine tool spindle. The actuating device includes a pressure piston which is arranged inside a housing for actuating the tool or workpiece tensioning jack. In order to provide a compact, space-saving actuating device enabling leakage fluid to be drained off in a simple manner, several interspaced continuous bores are arranged concentrically around a center axis in a side wall of the housing. Pressure plungers which are axially displaceable with the aid of the pressure piston are disposed therein and the housing contains at least one leakage channel with a section extending between the pressure plungers in a radially outer direction.
Due to the interspaced placement of the pressure plungers there will be space between them for the passage of one or more leakage bores or channels, into which any leakage fluid can flow off without back-pressure and it can be collected there or removed through corresponding lines. In particular in the vertical position of a machine tool spindle, the leakage fluid will flow by gravity downward and can be released at appropriate intervals or it can be moved off continuously through suitable lines as needed. The actuating device according to this invention is a particularly compact device and is thus also highly suited for machine tools with little available space.
For example, in a simple design and low-cost embodiment, the housing contains an inner housing part and an outer housing part securely attached to it such that an annular compression space for the pressure piston is defined. The leakage channel is formed preferably by bores which run parallel and perpendicular to the center axis of the housing. The bores can be sealed at their outward open ends by stopper plugs or drain screws or be connected to corresponding outlet lines.
Within the housing of the actuating device there is a rotary lead through for the inlet of a working fluid and/or cleaning fluid for the machine tool spindle which is rotating during operation. The rotary lead through is located preferably in a separate housing and can thus be installed or removed in a simple manner.
In addition, an air inlet channel for the cleaning of clamping surfaces or such can be provided in the housing of the actuating device.